This invention relates to processes and arrangements for monitoring and/or controlling charging of a modular battery, particularly in battery powered vehicles.
Electric vehicles which derive their power from rechargeable batteries, particularly from lead storage batteries connected in series, are already used for a variety of purposes. Such environmentally friendly electric power systems are beginning to gain increasing acceptance in road vehicles.
A significant problem encountered in such applications is monitoring the operational readiness of the battery modules and displaying indications of their state of readiness.
Even in other applications of batteries, for instance starter batteries for vehicles, the condition of the battery charge and an appropriate indication of that condition is important to a user. A large number of different processes for determining the operational condition of a battery are known.
For example, German Offenlegungsschrift No. 37 06 076 discloses the determination of the density of the battery acid for ascertaining the charge condition of the battery. This process is relatively costly for continuous detection and indication by a remote indicator.
In addition, U.S. Pat. No. 5,598,088 discloses a process for determining the charge condition of a battery from a charge balance by evaluating the charging current and the discharge current. In order to obtain as precise an indication of the battery charge condition as possible, additional corrections are applied which take into account the magnitude of the current, the temperature, and the age of the battery. In a similar process disclosed in U.S. Pat. No. 4,888,716, in which the service life of a motor vehicle battery is also determined and indicated, the terminal voltage, the charging and discharge current, and the temperature of a battery are detected and processed in an evaluation circuit and the result is displayed in an indicator unit.
German Offenlegingsschrift No. 37 06 076 also discloses a process in which the terminal voltage of a battery is sampled at discrete time intervals and the result is compared with values of a characteristic curve to determine the charge condition of the battery.
U.S. Pat. No. 5,635,820 describes a process for controlling the charging of a battery for an electric vehicle in which the battery temperature, the battery voltage and the charging current are detected and evaluated in a charge control device.
In the prior art battery monitoring and charge control systems mentioned above, measurement transducers are required on the battery or the battery modules and cells for detecting the necessary measurement data and, in addition to the power cables for the battery, signal lines which are electrically isolated from the power cables of the battery extend from the measurement transducers to the control and evaluation circuits. Consequently, a high expenditure is required for signal lines, especially for modular batteries such as those used in electric vehicles.
German Patent No. 41 05 369 discloses a charge condition indicator arrangement for a battery in a remote control transmitter for information processing devices, particularly for consumer electronics devices such as radio or television units or video recorders. In this arrangement, measurement data for determining the charge condition of the battery are detected in the remote control transmitter and transmitted without wires via a transmission medium such as infrared light, ultrasound or electromagnetic waves to the device to be controlled. The device to be controlled contains an evaluation circuit and a display element to indicate the battery charge condition. Such wireless transmission of measurement data detected at the battery to an evaluation unit is only possible under favorable conditions, and in particular is not suitable for a motor vehicle.